Managing Chronic Laminitis: Form and Function

The visible signs of chronic laminitis are enough to break any horse owner's heart--the dished, ridged hoof walls, the uncomfortable gait. But what's at the heart of the visible clinical signs, and, once a horse has progressed to this stage, can we do anything to significantly improve his quality of life?

Chris Pollitt, BVSc, PhD, head of the Australian Equine Laminitis Research Unit at the University of Queensland, discussed lessons he's learned from years of researching and managing chronic laminitis at the fourth annual Promoting Excellence Symposium of the Florida Association of Equine Practitioners (FAEP). The meeting was held Sept. 25-27, 2008, in San Juan, Puerto Rico.

Chronic laminitis encompasses the lingering aftereffects of the acute phase. In chronic laminitis the distal phalanx (the bone within the hoof capsule, also known as P3 or the coffin bone) has displaced. He said that as we watch laminitis progress via radiographs, we can see the toe rotating downward, a change that often causes significant remodeling.

Pollitt explained that this remodeling is caused by a multitude of factors working in conjunction. First, the weight of the horse pushes down on the bone and strains the already-inflamed lamellae (the Velcro-like fibers that secure the bone to the inside of the hoof capsule). These tear, allowing the bone to pull away. But along with this, the ongoing growth of the hoof occurs differently than it did before the laminitis first developed.

Tubules of horn growing down from the coronet band are now kinked. They no longer grow in a straight line--instead they grow inward, driving a wedge between the wall and bone. This is visible externally as the telltale ridges or rings that can be seen on lamintic hooves--it looks as if someone has placed a rubber band around the hoof. Pollitt noted that this tissue can recover and straighten itself up over time. At the same time the distal sole grows inward, further driving this wedge and forcing the hoof to continue growing in this distorted position.

The effects of this inward-growing horn can cause trauma to the distal phalanx, seen as excavation of the bone and significant remodeling. Eventually, the tip of the bone can completely wear away.

Pollitt noted that these ingrowing wedges are not typically seen before six weeks after the primary laminitic event. If you can get the horse to six weeks, you might not need to take drastic action. But if bony remodeling is evident, it's time to start working on that hoof.

So what can be done about it? Pollitt said at this point it's "chasing a horse that's already bolted."

The easiest way to make horses with bony remodeling feel more comfortable is to support the back of the foot--but at some point you also have to address the distorted tubular growth.

A strategic hoof resection (removal of hoof wall) might help some of these cases significantly, alleviating the pressure on the bone caused by ingrowing horn and re-establishing normal growth. Pollitt noted that venograms taken after resection show markedly improved uptake of blood in the foot (indicating improved circulation) as pressure on the venous structures within the hoof are relieved.

Pollitt noted that some horses might also benefit from a deep flexor tenotomy (surgically severing the deep digital flexor tendon), but the decision should made on a case-by-case basis.

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